(1) Field of the Invention
The present invention relates to gear change mechanisms and more particularly to such mechanisms employing dog clutches. Mechanisms according to the invention may be found useful in a variety of vehicular applications or in other machinery where a simple, robust and compact gearbox is required, one particular application being for a battle tank, bulldozer or other skid steered vehicle equipped with a drive configuration as described in WO-02/083483.
(2) Description of the Art
Constant-mesh gearboxes commonly employ dog clutches in the selection of different gear ratios. In a typical arrangement a gear selector hub is splined on an output shaft with freedom to slide axially along the shaft but so that the shaft must always rotate with the selector hub. Gears driven by the engine or other prime mover at different ratios are located coaxially to either side of the selector hub. The confronting faces of the selector hub and gears are formed with complementary axial projections and/or indentations (dogs) so that when the hub is slid, by an associated operating mechanism, in either direction from a central neutral position towards one of the gears, the respective dogs on the hub and gear will engage to transmit torque to the hub and output shaft from the selected gear at its respective ratio. This is a simple, robust and effective mechanism but necessarily occupies significant space in the axial direction due to the spacing of the gears, the provision of the dogs at opposite ends of the selector hub and the room required for the selector hub to shuttle between the gears.